This invention relates to a glass-vinyon material suitable for use as a separator material in reserve-primary zinc/air batteries at temperatures ranging from about -40.degree. C. to 50.degree. C.
It has been found that separator materials commonly used in zinc/air batteries do not wet readily when placed in contact with alkaline electrolyte at low temperatures i.e. of the order of about -40.degree. C. This problem is evident by the very long time required for the battery to reach an operational voltage after activation at -40.degree. C. Another problem associated with some of these materials is shrinkage or tearing during use at the higher battery operating temperatures typical of a battery during discharge at 50.degree. C.
One such separator material is Dynel, a Trade Mark for a copolymer of vinyl chloride and acrylonitrile in the form of a textile fibre. It was found that the very long time required for the battery to reach an operational voltage after activation at -40.degree. C. was due to the poor wettability of the Dynel separator at that temperature. If the battery was activated at room temperature, cooled to -40.degree. C. and then put on load, the working voltage was attained instantaneously. However, if the 33% KOH electrolyte at -40.degree. C. was added to a battery at the same temperature, the time required for the battery to come up to open circuit voltage (OCV) was about five minutes and the voltage decreased below the minimum acceptable level upon application of the load and did not recover for a further ten to fifteen minutes. These observations were unexpected as a number of commercially available Dynel, polypropylene and nylon materials have been used successfully as separators in zinc/air batteries. However, in the normal configuration of the reserve-primary zinc/air, the battery is activated by the addition of water which forms the electrolyte by leaching out powdered KOH from the porous zinc anode. Thus activation at temperatures below the freezing point of water is not possible.
Attempts to overcome this wettability problem have been made by substituting cellulose filter paper for the Dynel separator, but during evaluation of the batteries it was found that the quality of the paper was not uniform. Some samples would shrink and tear when wetted with electrolyte allowing the formation of anode to cathode short circuits.